Grip strengthener



FIG. 1 is a perspective elevation view of a grip strengthener showing my new design;

FIG. 2 is a bottom plan view thereof;

FIG. 3 is a top plan view thereof;

FIG. 4 is a left side elevation view thereof;

FIG. 5 is a right side elevation view thereof;

FIG. 6 is a front elevation view thereof; and,

FIG. 7 is a rear elevation view thereof. 

CLAIM The ornamental design for a grip strengthener, as shown and described. 